The present invention relates to multilevel coded modulation useful, for example, in voiceband data transmission (e.g., modem) applications.
As used herein, the term "multilevel coded modulation" refers to arrangements in which input data is divided into two or more streams which are individually encoded using respective redundancy codes. The coded outputs are then used jointly to select channel symbols from a predetermined signal constellation for transmission over a communication channel, such as a voiceband telephone channel. The principal advantage of adopting a multilevel coded modulation approach is that it provides the system designer with increased flexibility in designing a coding scheme which provides desired levels of error-rate performance, or "coding gain," while meeting various constraints on code complexity and decoding delay. Illustrative articles describing multilevel codes are: A. Ushirokawa et al, "Multilevel Codes for High-Speed Voiceband Data Modem," Proc. of IEEE Globecom 1989, pp. 1971-5; J. Wu et al, "Multi-Level Multidimensional Trellis Codes," International Symposium of Information Theory, Abstracts of Papers, sponsored by IEEE Information Theory Society, 1990, p. 110; and Pottie et al, "Multilevel Codes Based on Partitioning," IEEE Transactions on Information Theory, Vol. 35, No. 1, January, 1989.